The present invention relates to improvements in metal halogen battery systems. More particularly the invention relates to a new hydrate storage device for zinc-chloride battery systems. The invention herein is particularly useful for mobile battery applications, e.g., for electric vehicles.
The electrical energy storage systems of the type referred to herein (e.g., a zinc chlorine battery system or other metal-halogen battery system) utilize a halogen hydrate as the source of a halogen component for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal discharge of the storage system. An aqueous electrolyte is employed for replenishing the supply of the halogen components as it becomes reduced at the positive electrode. The electrolyte contains the dissolved ions of the oxidized metal and the reduced halogen and is circulated between the electrode area and a storage area containing halogen hydrate, which progressively decomposes during a normal discharge of the electrical energy system, liberating additional elemental halogen to be consumed at the positive electrode.
The state of the art in electrical energy storage systems or battery systems of this type is described in patents owned by the same assignee as the present invention, such as Symons U.S. Pat. No. 3,713,888; Symons U.S. Pat. No. 3,809,578 entitled "Process for Forming and Storing Halogen Hydrate in a Battery"; and Bjorkman U.S. Pat. No. 3,814,630 entitled "Filter/Store For Electric Energy Storage Device"; and, in commonly assigned copending Bjorkman U.S. patent application Ser. No. 368,892 filed Apr. 16, 1982. Such systems are also described in published reports prepared by the assignee herein such as "Zinc-Chloride Electric Engine Unit For Four Passenger Electric Vehicle" by J. Kiwalle et al. of Energy Development Associates. The specific teachings of the aforementioned cited reference are incorporated herein by reference. Reference is also made to commonly assigned copending application Ser. No. 343,904 filed Jan. 29, 1982 entitled "Metal Halogen Battery System", the disclosure of which is incorporated herein by reference.
The basic operation of a zinc chloride battery system is as follows. In charge, an electrolyte pump delivers aqueous electrolyte to pockets between pairs of porous graphite-chlorine electrodes in a battery stack comprised of a plurality of cells. The electrolyte passes through the porous chlorine electrodes into a chamber between opposite polarity electrodes, flows up between the electrodes, then flows back into the battery sump. Chlorine gas liberated from porous graphite electrode substrates is pumped by a gas pump, and before entering the gas pump, the chlorine is mixed with electrolyte chilled by a chiller unit. The chlorine and chilled electrolyte are mixed in the gas pump, chlorine hydrate forms, and the chlorine hydrate-electrolyte mixture is deposited in the store. In discharge, chlorine is liberated from hydrate by decomposition of chlorine hydrate in the store by injection of warm electrolyte from the sump. On development of the required chlorine gas pressure in the store, the chlorine is injected and mixed with and dissolved in the electrolyte, which is then fed to the porous electrodes in the battery stack. The battery stack is then discharged, wherein the electrode dissolution of zinc occurs at the zinc electrode, reduction of the dissolved chlorine occurs at the chlorine electrode, power is available from the battery terminals, and zinc chloride is formed in the electrolyte by reaction of zinc and chlorine to form zinc chloride.
There have been certain weaknesses in prior systems directed toward hydrate storage devices for mobile metal halogen battery applications. For example, prior designs and concepts for hydrate storage in mobile systems employed multiple nozzles and multiple filters that are staged for operation at various pressures, and various liquid/gas separation methods. Although these prior designs accomplished reasonably effective hydrate storage, they also had operational shortcomings as applied to mobile applications. These shortcomings were: (1) excessive liquid transfer from the hydrate store to the stack compartment during the charge cycle resulting in flooding of the stack sump; (2) insufficient gas-liquid separation resulting in periodic gas-out of the hydrate formation pump; (3) the multiple nozzles concept employed resulted, in many instances, in partial plugging which resulted in operational difficulties and reduced hydrate storage density; and, (4) staged multiple filters increased the functional complexity of the prior devices and also led to improper liquid separation and gassing problems.
Accordingly it is one object of this invention to provide a novel and unique halogen hydrate storage device for mobile battery systems. Other objects, features and advantages of the invention will become apparent from the description herein, from the drawings, and from the appended claims.